The manufacturing of rimless spectacles comprises the attachment of the temples and the nose-bridge directly onto the ophthalmic lens. This generally requires drilling a through-hole in at least two points of the ophthalmic lenses in the peripheral region thereof. A common problem associated with rimless spectacles is the incidence of cracking and crazing in the lens during the drilling process, and the propagation of the cracks during the mounting of the temples or nose-bridge or and/or during the subsequent daily use of the spectacles.
One approach to reducing the incidence of cracking flaws associated with rimless spectacles is to employ lenses composed of selected materials having an increased resistance to such flaws as disclosed in U.S. Pat. No. 7,135,545.
U.S. Pat. No. 7,726,808 discloses polishing the borehole's side-wall with an abrasive wire so as to eliminate the micro-cracks and crazes, thereby preventing propagation thereof in the lens during mounting and use.
It is an object of the present invention to further improve the drilling ability or drilling resistance of organic lens substrates, by laminating onto said lens substrate an impact-absorbing thermoplastic film via an adhesive layer. The present invention is based on the discovery that such a film efficiently absorbs the drilling stress only if its elastic modulus has a minimum value of about 3 GPa and if it sticks to the lens substrate with a minimum adhesion strength. As a matter of fact, the Applicants observed that when thermoplastic films having a high enough elastic modulus were laminated onto ophthalmic lenses having a final anti-smudge overcoat, chipping during drilling could not be efficiently prevented.